Research Of Composite Solid Polymer Electrolytes Based On Polyethylene Glycol

All-solid-state lithium batteries have attracted much attention because of their high safety,and solid-state electrolytes,as one of the core structures of all-solid-state lithium batteries,are related to the advantages and disadvantages of all-solid-state lithium battery devices.In recent years,solid-state polymer electrolytes have been used as solid-state electrolytes for research due to their easy film formation and light mass,but their poor mechanical properties and low lithium ion conductivity also hinder their practical applications.In this paper,polyethylene glycol（PEG/PEO）was used as the matrix and modified by adding ethyl fiber,nano-SiC and PPC and nano-BTO and PPC to it,so that the crystallinity of the polyethylene glycol-based composite solid state electrolyte was effectively reduced and its mechanical and electrochemical properties was improved significantly.Meanwhile,the corresponding composite cathodes were prepared according to the characteristics of different composite solid-state electrolytes to improve the solid-solid interface contact problem in solid-state lithium batteries,which enhanced the cycling performance of the all-solid-state battery.（1）A composite solid polymer electrolyte was prepared by polycondensation using polyethylene glycol（PEG）as the matrix,ethyl cellulose as the organic additive,and LiTFSI as the lithium salt.And the mechanical and electrochemical properties of the solid-state electrolyte were optimized by changing the addition amount of ethyl cellulose.The solid state electrolyte（SPE-CP1）with the addition amount of ethyl cellulose of PEG:ethyl cellulose=3:1 possessed better mechanical strength and electrochemical properties.The corresponding composite cathode was also prepared,allowing the all-solid-state lithium battery using SPE-CP1 to be cycled stably for 30cycles with a discharge capacity retention rate of 92%（test temperature:60°C,multiplicity:0.1 C）.（2）A solid state polymer electrolyte with higher mechanical and electrochemical properties was prepared by a one-step condensation method using PEG as the matrix,nano-SiC as the modifier,PPC as the secondary modifier,and then LiTFSI as the lithium salt.Its thermal stability showed good performance,and the ionic conductivity was greatly improved relative to the unmodified solid-state electrolyte,which is5.60×10^-5 S/cm at room temperature of 30°C and 2.19×10^-4 S/cm at the operating temperature of 60℃.The all-solid-state lithium battery using PEG-SIC（PPC）solid-state electrolyte could be cycled for more than 55 cycles（test conditions as above）,and the discharge capacity of 160 m Ah/g with a retention rate close to 99%.（3）A composite solid state polymer electrolyte was prepared by adding modified ferroelectric ceramic material nano-BaTO₃ with polypropylene carbonate（PPC）using PEO as the substrate and Li TSFI as the lithium salt,and the electrochemical performance of the solid state electrolyte was analyzed by controlling the molecular weight of PEO and the addition of lithium salt.The composite solid state electrolyte possessed well overall performance with the addition of BTO and PPC:PEO:BTO:PPC=1:0.5:1,PEO molecular weight:1 million,and lithium salt addition:[EO]:Li=16:1,and its ionic conductivity was 3.19×10^-5 S/cm at room temperature of25℃and 4.14×10^-4 S/cm at 60℃.By preparing the corresponding composite cathode,the all-solid-state battery with the composite electrolyte was allowed to cycle stably for more than 40 cycles（test conditions as above）with an initial discharge capacity of 152.0 m Ah/g and a capacity retention rate of 89%.